From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: PCI SERR NMI may cause Xen to deadlock Date: Tue, 31 Jan 2012 17:09:56 +0000 Message-ID: References: <4F2818C7.1050702@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4F2818C7.1050702@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: David Vrabel , "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org On 31/01/2012 16:37, "David Vrabel" wrote: > If a PCI System Error (SERR) is asserted it causes an NMI. If this NMI > occurs while the CPU is in printk() then Xen may deadlock as > pci_serr_error() calls console_force_unlock() which screws up the > console lock. > > I don't think removing the console_force_unlock() is sufficient as it > looks like printk() is unsafe to call from NMI context. We would like > keep the diagnostic. Does the following (untested) patch to defer the > printk() to a softirq look like a valid approach? Yes, if the NMI is non-fatal then console_force_unlock() cannot be used. So your only other option is to defer the printk. -- Keir > I also considered passing the NMI to dom0 (like other NMIs are) but I > couldn't see how NMIs were handled in the current upstream pv-ops kernels. > > diff -r e2722b24dc09 xen/arch/x86/traps.c > --- a/xen/arch/x86/traps.c Thu Jan 26 17:43:31 2012 +0000 > +++ b/xen/arch/x86/traps.c Tue Jan 31 16:28:45 2012 +0000 > @@ -3173,6 +3173,11 @@ static void nmi_mce_softirq(void) > st->vcpu = NULL; > } > > +static void pci_serr_softirq(void) > +{ > + printk("\n\nNMI - PCI system error (SERR)\n"); > +} > + > void async_exception_cleanup(struct vcpu *curr) > { > int trap; > @@ -3259,10 +3264,11 @@ static void nmi_dom0_report(unsigned int > > static void pci_serr_error(struct cpu_user_regs *regs) > { > - console_force_unlock(); > - printk("\n\nNMI - PCI system error (SERR)\n"); > - > outb((inb(0x61) & 0x0f) | 0x04, 0x61); /* clear-and-disable the PCI > SERR error line. */ > + > + /* Would like to print a diagnostic here but can't call printk() > + from NMI context -- raise a softirq instead. */ > + raise_softirq(PCI_SERR_SOFTIRQ); > } > > static void io_check_error(struct cpu_user_regs *regs) > @@ -3563,6 +3569,7 @@ void __init trap_init(void) > cpu_init(); > > open_softirq(NMI_MCE_SOFTIRQ, nmi_mce_softirq); > + open_softirq(PCI_SERR_SOFTIRQ, pci_serr_softirq); > } > > long register_guest_nmi_callback(unsigned long address) > diff -r e2722b24dc09 xen/include/asm-x86/softirq.h > --- a/xen/include/asm-x86/softirq.h Thu Jan 26 17:43:31 2012 +0000 > +++ b/xen/include/asm-x86/softirq.h Tue Jan 31 16:28:45 2012 +0000 > @@ -6,6 +6,7 @@ > #define VCPU_KICK_SOFTIRQ (NR_COMMON_SOFTIRQS + 2) > > #define MACHINE_CHECK_SOFTIRQ (NR_COMMON_SOFTIRQS + 3) > -#define NR_ARCH_SOFTIRQS 4 > +#define PCI_SERR_SOFTIRQ (NR_COMMON_SOFTIRQS + 4) > +#define NR_ARCH_SOFTIRQS 5 > > #endif /* __ASM_SOFTIRQ_H__ */ > > David > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel